1. Field of the Invention
The present invention relates to an improved infusion apparatus.
2. Description of the Prior Art
FIG. 4 is a simplified block diagram of a conventional infusion apparatus and FIG. 5 is a sectional view of an infusion pump. Referring to FIG. 4, a conventional infusion apparatus has an infusion pump 2 driven by a motor 1 to administer medication to a patient. The infusion pump 2 is constructed as shown in FIG. 5, and includes a housing 11, bearings 12, a shaft 13, cams 14, fingers 15, and a pressure plate 16. The aforementioned infusion pump 2 delivers fluid such as a solution through an administration tube 17 in the following manner.
When the shaft 13 is driven to rotate by the motor 1 (refer to FIG. 4), a plurality of cams 14, 14, . . . mounted around the shaft 13 rotate. Each cam 14 has a circular form and is secured eccentrically to the shaft 13 so that it has a maximum radius a.sub.1 and a minimum radius a.sub.2. In the present example, eight of the above-mentioned type cams 14 are mounted around the shaft 13.
Then, the cams 14 mounted around the shaft 13 are shifted in angle between adjacent ones by 45.degree. (360.degree./8). Consequently, the cams 14 are arranged so that the cams 14 gradually change their radii each from the maximum radius a.sub.1 to the minimum radius a.sub.2 and then from the minimum radius a.sub.2 to the maximum radius a.sub.1 toward the pressure plate 16 in a phase shift manner. With the above-mentioned arrangement, the cams 14 . . . rotate in company with the rotation of the shaft 13 to achieve a wave-like movement of the circumferences of the cams 14.
The cams 14 are rotatably inserted in the aforementioned fingers 15. When the shaft 13 rotates to rotate the cams 14, end portions 15a of the fingers 15 slide in a direction perpendicular to the shaft 13 synchronously with the movement in radial direction of the cams 14. Therefore, by arranging in a direction perpendicular to the pressure plate 16 the end portions 15a, of the eight fingers in which the eight cams 14 are inserted, the end portions 15a of the eight fingers 15, move in a wave-like manner in accordance with the rotation of the cams 14. In other words, the end portions 15a, of the eight fingers move in a peristaltic manner in company with the rotation of the shaft 13.
Between the end portions 15a of the fingers 15 and the pressure plate 16 is interposed the administration tube 17. When each of the end portions 15a of the eight fingers 15, 15, . . . is put in a position closest to the administration tube 17, the end portion 15a of the finger 15 presses the administration tube 17. Then by rotating the shaft 13 to peristaltically move the end portions 15a of the fingers 15, 15, the end portions 15a of the fingers 15, consecutively occlude the administration tube 17 from an upper portion to a lower portion to push downward the medication fluid through the administration tube 17 to thereby transfer the medication fluid.
The infusion pump 2 having the above-mentioned construction is driven by the motor 1 under the control of a controller 3 as shown in FIG. 4.
FIG. 6 shows a detailed block diagram of the controller 3. The following describes the controller 3 with reference to FIG. 6.
A key panel 21 includes various operation keys such as numeral keys for inputting values of fluid infusion rate, volume to be infused (referred to as VTBI hereinafter), and the like for operating the infusion pump 2, control keys for input assistance, a start key for starting a fluid infusion, a stop key for stopping the fluid infusion, and a call-up key for displaying volume infused (referred to as VI hereinafter) and the like.
Data of the fluid infusion rate and VTBI input from the key panel 21 are displayed on a programming display section 22 for confirmation by a doctor or nurse.
After the various data are input in a manner as described above, fluid infusion is initiated by the start key. Then the aforementioned motor 1, which is a stepping motor, is driven by a motor driving circuit 23 to rotate the shaft 13 of the infusion pump 2 (refer to FIG. 4) and thereby peristaltically move the fingers 15 to effect fluid infusion.
A rotation amount of the infusion pump 2 is detected by a pump rotation detector 4 described in detail hereinafter, and a CPU (Central Processing Unit) 24 detects the fluid infusion rate according to a detection result from the pump rotation detector 4.
During the fluid infusion operation, a variety of safety devices described as follows are used to safely operate the infusion apparatus.
First, an upstream occlusion sensor 25 detects a pressure-reduction state within the administration tube 17 due to the occurrence of occlusion (e.g., clogged filter) between a medical solution container (not shown) containing a medication fluid and the infusion pump 2, and outputs a digital signal representing the occlusion/non-occlusion state.
A downstream occlusion sensor 26 detects a pressure-rise condition within the administration tube 17 due to the occurrence of occlusion between the infusion pump 2 and the patient, and outputs a digital signal representing the occlusion/non-occlusion state.
An air bubble detector 27 detects an air bubble inside the administration tube 17, and outputs an analog signal representing the size of the air bubble.
A door opening detector 28 detects that a door of the infusion apparatus is open, and outputs a digital signal representing the open/closed state of the door. The inner surface of the door of the infusion apparatus concurrently serves as the pressure plate 16. Inside the door is provided the upstream occlusion sensor 25, the downstream occlusion sensor 26, the air bubble detector 27, and the like. The infusion apparatus does not function when the door is open, and therefore the fact that the door is open must be securely detected when the infusion apparatus is in operation.
A battery voltage detector 29 detects the voltage level of a battery and outputs an analog signal representing the voltage level.
An analog-to-digital (A/D) converter 30 takes in an analog signal representing the motor current level from the motor driving circuit 23, the analog signal representing the size of the air bubble from the air bubble detector 27, and the analog signal representing the voltage level from the battery voltage detector 29, and converts the analog signals into digital signals to output the resulting digital signals to the CPU 24.
Thus the CPU 24 can detect the existence of an air bubble having a size greater than a prescribed value and an abnormal drop of the battery voltage based on the digital signals from the A/D converter 30. Furthermore, the CPU 24 detects the occlusion of a fluid transfer system and a door open state based on the digital signals from the upstream occlusion sensor 25, the downstream occlusion sensor 26, and the door opening detector 28.
An alarm/alert display section 31 is driven by the CPU 24 to display alarm or alert messages of the upstream occlusion condition, downstream occlusion condition, the existence of an air bubble greater than a prescribed size, an open condition of the door, and an abnormal drop of the battery voltage.
Furthermore, a buzzer 33 is driven by a alarm/alert buzzer driving circuit 32 to inform the doctor or nurse of the alarm/alert by means of the buzzer sound.
A panel lock switch 34 serves to render the keys of the key panel 21 and the power key input-inhibited so that the infusion apparatus will not be operated by any person other than doctors or nurses.
An operation indicator lamp 35 indicates that the apparatus is currently in a state of fluid infusion operation, alarm, or alert.
A RAM (Random Access Memory) 7 stores a variety of data to be used for operation of the CPU 24. In the RAM 7, a counter whose initial value is the VTBI input from the key panel 21 and an edge counter for counting a rotation amount of the infusion pump 2 as described hereinafter and VI are set up.
A ROM (Read Only Memory) 36 stores a program for operating the controller 3.
In order to inform the doctor or nurse of the VTBI or volume to be infused (i.e., the current scheduled fluid volume) and the VI or total volume infused (i.e., the current cumulation volume) while administering medication fluid to a patient by means of the infusion apparatus, it is necessary to measure the current fluid delivery rate of the infusion pump 2.
Conventionally, the measurement of the fluid delivery rate of the infusion pump 2 has been performed by means of the aforementioned pump rotation detector 4, the controller 3, and the RAM 7 in the following manner.
Referring to FIG. 4, the pump rotation detector 4 mainly includes a slit disk 6 mounted to the shaft 13 at an end opposite to the motor 1 of the infusion pump 2 and a sensor 5 which is mounted so that it extends over both surfaces of a peripheral portion of the slit disk 6. At the peripheral portions of the slit disk 6 are formed a plurality of slits (not shown) extending radially at regular intervals to the circumferential direction. The sensor 5 detects light which has passed through the slit portion of the slit disk 6 rotating, and outputs a light detection signal.
The light detection signal output from the sensor 5 in a manner as described above is transmitted to the controller 3.
Then the controller 3 detects the amount of change from the slit portion to the non-slit portion or from the non-slit portion to the slit portion (referred to as the "rotation amount" hereinafter) of the rotating slit disk 6 based on the light detection signal. Based on the detected rotation amount, the fluid infusion rate, i.e. the fluid delivery rate is detected.
FIG. 7 shows a flowchart of the fluid infusion rate detection operation executed by the controller 3. The following describes the fluid infusion rate detection operation with reference to FIG. 7.
It is noted that an incremental unit (i.e., the amount of fluid flow made in one operation cycle of the infusion pump 2) is assumed to be 0.1 ml in the present apparatus.
When the aforementioned motor 1 is rotating, the count value of an edge counter is incremented every time each of two side edges of a sector passes through the sensor 5 based on the light detection signal from the sensor 5 (step S1 through step S3).
When the resulting edge count value reaches a preset edge count value corresponding to the incremental unit of 0.1 ml (i.e., a value two times as many as the slit amount provided in the slit disk 6), the count value of a VTBI (i.e., volume to be infused) counter set in the RAM 7 is decreased by the incremental unit while the count value of a VI (i.e., volume infused) counter is increased by the incremental unit. Thereafter, the count value of the edge counter is cleared (step S4 and step S5).
When the count value of the VTBI counter counted down is not "0", the program flow returns to step S1 to enter into a process of measuring the next unit flow. Otherwise, the fluid delivery rate detection operation ends (step S6).
Then the incremented count values of the VTBI counter and the VI counter are read out from the RAM 7 as needed, and the VTBI and the VI are displayed on a display unit 8.
Because the fingers 15 move peristaltically downward in the infusion pump 2, there is an intermission in medication fluid delivery after the lowermost finger 15 has finished pressing the administration tube 17 until the second uppermost finger 15 begins to press the administration tube 17.
The above-mentioned intermission in medication fluid delivery is referred to as the "dead band" and the period for which the medication fluid is flowing is referred to as the "live band" hereinafter.
The aforementioned conventional measurement of the fluid delivery rate has been performed by continuously detecting the rotation amount of the rotating slit disk 6 by means of the aforementioned controller 3 to detect the incremental unit, and therefore the incremental unit has been detected on the assumption that fluid delivery is effected even in the dead band.
Consequently, there has been a problem that the VTBI and the VI displayed on the display unit 8 differ from the actual values.
When the fluid delivery rate to be detected is not smaller than the fluid flow in one operation cycle of the infusion pump 2 (incremental unit), the fluid delivery rate can be detected with certain accuracy by taking into account the loss in fluid delivery due to the dead band in one operation cycle of the shaft 13 of the infusion pump 2. However, when the fluid delivery rate to be detected is smaller than the above-mentioned unit flow, there is no way for perceiving how much edges related to the dead band exist in the detected edges. Therefore, it is impossible to detect any fluid delivery rate smaller than the unit flow.